Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

963
FXUS63 KLOT 272336
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
536 PM CST Fri Feb 27 2026

.KEY MESSAGES...

- A pair of storm systems may bring accumulating snow to parts
  of the area this weekend, favoring areas near and north of the
  Wisconsin state line Saturday afternoon, and areas well south
  of Interstate 80 Sunday night. Much of the area may miss out
  on snow.

- A pattern change toward warmer and wetter conditions is
  expected through the first few weeks of March.

&&

.DISCUSSION...
Issued at 115 PM CST Fri Feb 27 2026

Through Sunday Morning:

Recent satellite imagery augmented by surface observations
depicts a vigorous upper-level shortwave and associated surface
low moving through central Ontario. Continued low-level
pressure falls ahead of the system is supporting aggressive warm
air advection across the Lower Great Lakes, which with mostly
sunny skies is resulting in temperatures climbing into the lower
60s. The combination of the warm and dry conditions atop
dormant vegetation will continue to support a threat for the
spread of brush and grass fires through the afternoon (have
noted several fires already in radar and satellite data as of
press time).

As the low pressure system moves toward Quebec tonight, a dry
cold front will move across the Lower Great Lakes and usher in
reality with falling temperatures and breezy northwest winds.
Lows will fall toward the upper 20s (northwest) to lower 30s
(southeast) as the baroclinic zone stalls across central
Illinois and Indiana.

By tomorrow morning, deep cyclonic upper-level flow will be
established across the Upper Great Lakes. Ensemble guidance
remains in agreement that an upper-level jet streak will nose
into the central Great Lakes by mid-morning and excite a
frontogenetical circulation within the low-level baroclinic
zone. With residual dry low-level air remaining in place across
northern Illinois and northwestern Indiana as well as the
positioning of the jet to move almost directly overhead (keeping
upper-level diffluence maximized to our north), a majority of
guidance keeps any measurable snow north of the Wisconsin state
line through much of the day on Saturday. So, will cautiously
trim PoPs to focus along the Wisconsin border. Highs will vary
quite a bit across the area tomorrow, with readings near the
freezing mark near the Wisconsin state line to around 40 degrees
along I-80 to the lower 50s along US-24.

Tomorrow afternoon and evening, an embedded shortwave embedded
within the cyclonic flow aloft will induce the development of a
low pressure system within the baroclinic zone somewhere in
central Illinois. HRRR/RAP guidance has trended far more
aggressive with the speed and strength at which the low deepens,
leading to a corresponding increase in flow along the backside
of the system as it moves into Indiana after dark. While the
upper-level cyclonic shear axis will remain well to our
northeast tomorrow evening, the increase in low-level flow and
associated shoreline convergence in tandem with falling 850mb
temperatures may be able to support low-topped lake effect snow
showers Saturday evening especially if HRRR/RAP solutions were
to verify. With an easterly component to the wind behind the
system, any snow showers may be prone to moving into
northeastern Illinois before shifting toward northwestern
Indiana Sunday morning. Given the marginal thermodynamics and a
lack of support from other guidance, am not quite ready to go
all-in on the idea of snow showers developing quite yet but will
nevertheless introduce low (20-30%) chances for snow showers
along the Lake Michigan shoreline Saturday night through Sunday
morning.

Borchardt

Sunday Afternoon Onward:

An expansive Canadian high will slide across the Upper Midwest
into the Great Lakes on Sunday. As it does, the next mid-level
short wave impulse will track east-southeastward along its
southwestern periphery, and along the southern periphery of the
low-level baroclinic zone, right into the Mid-Mississippi Valley
region by Sunday night. Overall, conditions continue to be
quite favorable for this to support a somewhat narrow corridor
of notable accumulating snowfall late Sunday into early Monday
somewhere across portions of the Midwest eastward into the Ohio
Valley. The primary uncertainty for our area is how far north
any accumulating snow will extend, especially considering it
will be fighting a progressively much dryer airmass with
northward extent. Recent ensemble trends have favored areas
farther south across central IL for this area of accumulating
snow. If these trends continue, little to no snow will fall
across northern IL and northwestern IN.

Otherwise, following a chilly period Sunday into Monday (highs
in the 30s Sunday and low 40s Monday), a significant large scale
weather pattern shift is expected this coming week. The pattern
will transition to the negative phase of the Pacific North
American (PNA) teleconnection pattern, which is characterized by
western CONUS mid and upper level troughing and eastern CONUS
ridging. While the day-to-day specifics of this pattern remain
somewhat unclear, there is above average forecast confidence
that this pattern will favor periods of active weather,
including notable rainfall amounts and thunderstorms, along with
above average temperatures through next weekend.

Our current forecast does advertise at least some lower end
chances for rain each day Tuesday through next weekend. In spite
of this, do not expected to be raining constantly, as there
will be periods of dry time. Our first favored period of rain is
late Monday night into Tuesday in association with increasing
warm air advection (isentropic upglide) setting up across a
surface frontal boundary downstream of an impulse traversing the
CO Rockies. There is a strong signal for rainfall during this
period, with roughly 70 to 90+ percent of the ensemble members
producing rain across a good portion of the area. Thereafter,
ensemble spread increases, particularly with the speed and
timing of the the next impulse expected to shift into the lower
Great Lakes region sometime Wednesday into Thursday. If the
slower solutions advertised by main of the ensemble suites pan
out, a good chuck of Wednesday could be dry before rain chances
increase again Wednesday night into Thursday.

Regardless of exactly how the mid to late week period evolves,
precipitable water of 250-300% of average/normal for early March
could certainly spell corridors of heavy rainfall and an
associated flooding threat. The extent (or lack thereof) of
embedded thunderstorms will likely play a role as well. Finally,
the exceptionally mild and moist cyclone warm sectors in the
upcoming pattern may also feature a threat for organized strong
to severe convection within in the general region.

KJB

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 536 PM CST Fri Feb 27 2026

Forecast concerns include...

Wind shift to northwest this evening.
Wind shift to northeast Saturday morning.
Low chance for light snow/flurries Saturday.
Possible mvfr cigs Saturday afternoon into Saturday evening.

Southwest winds are steadily diminishing with sunset currently
and will shift to northwest this evening. Some gusts into the
15-20kt range will still be possible both ahead and behind the
front with speeds/gusts gradually diminishing in the predawn
hours. Winds will then shift northeasterly Saturday morning.
Speeds will increase into the 10-12kt range by afternoon with
gusts into the 15-20kt range expected to develop by early
Saturday evening.

Snow is expected to remain mainly north of the terminals on
Saturday with a low chance for light snow or flurries along and
north of a RFD/ORD line. Maintained prob mention at RFD for
midday but confidence continues to decrease for the rest of the
terminals and removed mention elsewhere.

Cigs are expected to trend down to low vfr by late Saturday
morning with at least patchy mvfr cigs possible Saturday
afternoon and then a better chance for mvfr cigs Saturday
evening, especially for the Chicago terminals and near Lake
Michigan, though only medium confidence. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 9 PM CST this evening for Winthrop
     Harbor IL to Burns Harbor IN.

     Small Craft Advisory from 2 PM Saturday to 3 PM CST Sunday for
     Winthrop Harbor IL to Burns Harbor IN.

     Small Craft Advisory until 3 PM CST Sunday for Burns Harbor to
     Michigan City IN.

&&

$$

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